Radio receiver



H." J. LOFTIS RADIO RECEIVER Filed March 5, 1950 A ril 14, 1936.

Patented Apr. 14, 1 936 UNITED STATES RADIO RECEIVER Homer J. Loftis, Dayton, Ohio, assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application March 3, 1930, Serial No. 432,756

1 Claim.

This invention relates to a radio signal amplifying device, and more particularly to an amplifying device embodying a detector stage.

An object of this invention is to change the 5 detector stage to a stage of audio frequency amplification. This has been accomplished by changing the bias of the grid with respect to the cathode, so that the thermionic tube ceases to function as a detector.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred embodiment of one form of the present invention is clearly shown.

In the drawing:

In the single figure a schematic diagram of a portion of a radio receiver has been disclosed.

In the drawing the reference numeral l indicates a stage of radio frequency amplification having its output connected to a detector circuit l2, feeding into a stage of audio frequency amplification l4, provided with an output terminal l6, which may be connected to another stage or stages of audio frequency amplification or to a reproducer such as a loud speaker. As the radio frequency stage and as the audio frequency stage forms no part of this invention, a detail description of each of these is not made.

The detector circuit [2 includes a thermionic tube I! having the control electrode l 8, a cathode 20, the anode 22, and in this particular modification, the heater element 24.

Although a three element .tube having an indirectly heated cathode has been disclosed, any other tube that may be used as a detector can be used within the purview of this invention.

Whenthe thermionic vacuum tube I1 is used as a detector the potential supplied to the control electrode 18 is substantially equal to ground in that, the difference of the potential between the control electrode l8 and ground is equal to the grid current times the resistance of the leads and the windings 28 which for all practical purposes may be ignored. The potential of the cathode 20, however, is much greater than ground for the reason that the anode current flowing from the anode 22 to the cathode 20 passes through the resistance 26 to ground. For this reason, the cathode 20 will have a potential that is considerable above the potential of the control electrode l8, as is well understood by those skilled in the art.

It is desirable at times to use the stage or stages of audio frequency amplification of a radio receiver as amplifiers for a phonograph pick-up.

The phonograph pick-up, conventionally shown at 41, may be connected to the terminals 40 and 42 by suitable leads 44 and 4B. When the lever or switch blade 50 is in the full line position as disclosed in the single figure the terminals 40 and 42 are each connected directly to ground, hence, the incoming signals from the phonograph pick-up has no effect upon the detector I2. When the switch blade or lever 50 is switched into the dot-dash position 52 by any suitable means, for example, by an automatic switch which is actuated when the tuning device of the radio receiver is completely detuned so that there is no incoming signal from the radio frequency amplifier ID, the phonograph pick-up will then be connected to the control electrode IB through the inductance 28. At the same time the resistance 54 will be connected to the cathode 20 to ground and in parallel with the resistance 26. I have found that a one-to-ten ratio of the resistance 54 to the resistance 26 gives good results for some types of tubes. From this it may be readily seen that the potential of the cathode 20 will be less than one-tenth of the potential after the resistance 54 is connected in parallel with the resistance 26 for the same anode current. In other words, the effectiveness of the grid bias will be greatly decreased so that the tube will function as an audio frequency amplifier instead of a detector. This will, as is well known to those versed in the art, greatly improve the amplification of this stage.

While the form of embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claim which follows.

What is claimed is as follows:

In a radio-phonograph combination, a relay having an input circuit and an output circuit and normally operating as a detector relay, said relay including a control electrode, a phonograph pick-up device connected in the relay input circuit, means for biasing said control electrode comprising an impedance device common to the input and output circuits of the relay, an auxiliary impedance element, a multi-position switch device and circuits associated with the switch device for simultaneously short circuiting the pickup device and adjusting the impedance device to give the relay circuit a detector operating characteristic when the switch is thrown in a predetermined position and simultaneously removing the short circuit from the piclc-up and shunting the auxiliary impedance element across the impedance device to give the relay an amplifier operating characteristic when the switch 5 is thrown in another predetermined position.

HOMER J. LOFTIS. 

